The invention relates to an offset press of the type comprising a frame, at least one plate cylinder, a press cylinder, and a blanket cylinder interposed between the plate cylinder and the press cylinder, and bearing assemblies carried by the frame and receiving the longitudinal ends of the cylinders so that each cylinder is free to rotate relative to the frame about a respective longitudinal central axis.
In such a press, each cylinder end is mounted in a frame via a rotary bearing assembly. Drive means serve to set the cylinders into rotation.
In operation, the plate carried by the plate cylinder is moistened and then inked. The plate transfers ink from its printing regions onto the blanket carried by the blanket cylinder. The blanket then transfers ink onto the paper to be printed which passes between the blanket cylinder and the press cylinder.
In order to be able to transfer the ink firstly from the plate to the blanket and secondly from the blanket to the paper, the plate cylinder, the blanket cylinder, and the press cylinder must press against one another in operation. The cylinders then exert radial bending forces on one another.
In order to prevent the cylinders deflecting too far under drive from these forces, which could prevent the press from operating properly, care is taken to ensure that each cylinder has a relatively small aspect ratio, i.e. that the length of each cylinder between its two end bearing assemblies divided by the diameter of the cylinder remains relatively small, and generally less than about 6.
Thus, the diameters of the cylinders in a press of the above-specified type are relatively large which leads to large weight and to manufacturing and installation costs that are relatively high.
This raises an additional problem for the plate cylinder which, because of its large circumference, makes it necessary either to use plates that are very long and are therefore complex to install, or else to install two plates each corresponding to half the circumference, likewise giving rise to high costs because of the larger number plates that need to be used in a given print run and because of the difficulties involved in installing two plates simultaneously on one plate cylinder.
An object of the invention is to resolve those problems by providing a press of the above-specified type which enables the diameter of at least one cylinder to be reduced and thus enables the cost associated with the press to be reduced.
To this end, the invention provides an offset press of the above-specified type, wherein each of the longitudinal ends of at least a first cylinder are received in first and second bearing assemblies, the second bearing assembly being spaced apart from the first bearing assembly along the longitudinal axis of the first cylinder.
In particular embodiments, the offset press may comprise one or more of the following characteristics taken singly or in any technically feasible combination:
the press comprises off-centering means for each end of the first cylinder for positioning the first bearing assembly eccentrically relative to the second bearing assembly;
the first bearing assembly is movable relative to the frame between a first position in which its eccentricity is reduced or zero, and a second position in which its eccentricity relative to the second bearing assembly is greater, and the off-centering means comprise displacement means for moving the first bearing assembly between its first and second positions;
the first bearing assembly is mounted to pivot relative to the frame about an axis that is substantially parallel to the axis of the second bearing assembly;
the displacement means comprise an actuator extending between the frame and the first bearing assembly;
for each end of the first cylinder, the displacement means are adjustable to enable the first bearing assembly to be moved into a position that is intermediate between its first and second positions;
the first cylinder is the plate cylinder; and
the plate cylinder is of diameter smaller than that of the blanket cylinder.